Advantages of multiple midwoofers? (e.g., MTM, 2.5-way...)

[Apfelsauce]

What are some of the advantages of using multiple woofers where otherwise you would just use one? Are the advantages somewhere other than in the low-end response? I can't see much drop in Fb or F3 for a given configuration... (All one has to go is double Vas, right? Save for the circuitry, of course - when one must account for changes to nominal impedance?)

[AllenB]

What about achieving a controlled and symmetrical vertical polar pattern?

[Wayne Parham]

You can also use multiple midwoofer sound sources to smooth peaks and notches caused by room modes and boundary reflections in the upper modal range, in the midbass to midrange. This 100-200Hz transition region is too high to be smoothed by muliple distant subwoofers, but can be greatly improved by blending sources spaced at a distance closer to wavelength scale at those frequencies. It can be done with "helper" woofers (like 2.5-way), blending mid and woofer in that region or with flanking subs. The key is to have at least two sound sources in this frequency range, spaced a couple feet apart, one closer to nearest boundary or boundaries than the other.

• Room modes, multisubs and flanking subs

[Arty]

one other approach is.. that You can connect the midwoofers in paralell, thisway You can improve the sensitivity. In other words, You may not have to pad the tweeter that mutch.
Basicly it improves overall system efficiency.

One can even sacrifice some of this newly gained efficiency to extend the low end response. This is done by a filter.(not realy a common practice as far as i know)
Or consider that You have more surface area, You need less excursion, therefore You have less distorsion. (mm sometimes this last point is not valid as it may just make no difference at all..)

Allso, every box has a baffle, and its effects may need to be compensated.
2.5 way designs can do this by rolling the 2nd woofer at a different freqvency.


In otherwords, done correctly it is a neat trick to improve compared to a single driver.
Done not so correctly and You end up with a lotta phase problems.

[PeteMcK]

Don't forget SAF...

[Jay]

From my experience, I don't like multiple driver, except when I need the most advantage of this arrangement, which has been stated by Arty:

1) High end midwoofer with stiff cone tends to have too much distortion. You can limit the midwoofer excursion (to lower the distortion) with dual midwoofer.

2) Resistor in series with tweeter will limit the tweeter dynamic. I never used L-Pad, only resistor before the first capacitor. If small value resistor is not possible, you need double woofer.